38 



HOLLAND: MICA DEPOSITS OF INDIA. 



Phlogopite. 



3 H 2 0. K„0. 7 MgO. A1„0 8 . . 

 7 Si0 2 . 



I A1 2 3 . 

 MgO . 

 K„0 . 



• 



• 



. 44 - 2 

 . io-8 

 • 29-4 

 . 99 





> H 2 . 



> Q 



■ 57 



The micas may thus be looked upon as silicates in different propor- 

 tions of alumina, the alkalies (mainly potash), iron and magnesia. 

 Arranging the bases according to their quantity and importance their 

 order is seen to be reversed in the two groups : — 



I. Alumino-alkaline. 



Silicates of 



Alumina, 

 ies. 



+ rtiumn 



\ Alkalie 



J Iron. 



^ Mnpnp 



II. Ferromagnesian. 



Silicates of 



Magnesia. 

 Iron. 

 Alkalies. 

 Alumina. 



Magnesia. 



Muscovite is by far the most important of the Indian micas and the 

 only one which has been worked to any serious extent, though the 

 other three chief varieties also occur in quantity. The following two 

 analyses of Indian mica, most probably from Bengal, shows the com- 

 position of the muscovite so largely mined and exported : — 









I. 



II. 



Si0 2 . . . 45'57 



4571 



AL0 3 , 







. 3 6 -72 



3657 



Fe,O a . 







■ °'95 



1-J9 



FeO . 







. 128 



ro7 



MgO . 







. 038 



071 



CaO . 







. 02 1 



0-46 



K 2 . 







. 8-8 1 



9'22 



Li,0 . 







. 19 



... 



Na,0 . 







062 



079 



H„0 . 







5'°5 



4'83 



F 



• 



0-15 



0'i2 









99'93 



IOC67 



Sp. Gr. = 2'83i Sp. Gr. = 2'83o 



I. Analysis by L. Sipocz. 1873, Tschermak's min. und petr. Mittheil, 



P-31- 

 II. Analysis by S. Blau . . Ibid. 1873, p. 32. 



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